You're still very young, so you really don't need to worry about any of this. You're making way more progress than you think.
Maybe you should give up on collaborations though, for a couple years. Focus on writing scripts, improving your craft. Branch out to short stories and poetry, lots of smaller projects for yourself. Do the same thing with drawing. Small projects made for practice and fun. You'll get better and better all on your own until suddenly one day you look at yourself and realize, "Holy crap I've improved so much."
If comics really are your passion, then practicing both writing (in all mediums, but especially scripts), and art (in many styles and different software) should be paramount here. Have fun with them both! But don't try to rush through trying to make the giant pro projects when it's too expensive and too expansive; it's just a road to frustration. Trust me on that one; a skilled enough internet stalker could very easily dig up 5 or 10 failed collab projects I had when I was 17 that were way too ambitious and took up way too much of my time. I really had much more fun working on smaller stuff later on.